Fix dark model bug when user directly visit page.html & post.html

_layouts/post.html

@@ -7,7 +7,7 @@ layout: compress
 
 {% include header.html %}
 
-<body>
+<body data-theme="{{ site.mode }}">
   {% include navbar.html %}
   <div class="wrapper post">
     <main class="page-content" aria-label="Content">